Water vortices can generate electricity in a sustainable, mostly-fish-friendly way. According to University of Michigan professor, Michael Bernitsas, water flowing past a cylindrical object creates vortices along the side. A vortex occurs on one side, then on the other, alternating back and forth. This can be destructive (as with oil rigs or the Tacoma Narrows Bridge). Bernitsas was working on ways to reduce or eliminate vortex-induced oscillations, when he realized that a better solution might be to *harness* the oscillations.
Bernitsas’ company, Vortex Hydro Energy, notes that VIVACE (Vortex Induced Vibrations Aquatic Clean Energy) can be produced in currents as slow as 2-4 knots. Most conventional turbines require at least four knots–and most rivers and ocean currents in the USA flow at 3 knots or less. VIVACE does not use turbines, so it is safer for fish.
(full post, with links, at So May We Be)